Liposomes are microscopic vesicles, which are generally spherical and have diameters ranging from about 25 to about 30,000 nm. They have concentric lipid bilayer structures consisting of closed concentric lamellae enclosing one or more aqueous-containing compartments. Liposomes are formed from lipid or lipid-like molecules having a lipophilic and hydrophilic moiety and can encapsulate various materials including biologically active materials and are widely used in drug delivery. Recent research has found that some liposomes can also perform as sensitive sensors for the detection of various analytes (see, e.g., Reichert et al., J. Am. Chem. Soc. 117:829 (1995); Spevak et al., J. Am. Chem. Soc. 115:1146 (1993); Charych et al., Science 261:585 (1993); and U.S. Pat. No. 6,103,217). Typically, liposomes are used in liquid, paste, creme, gel, and lotion formulations. To date, liposomes are rarely used in an implantable device for localized drug delivery within a human body, partly because solid-state materials containing intact liposomes are difficult to make or not biocompatible and partly because liposomes are difficult to be immobilized to the surface of a substrate. A few methods have been developed that overcome some of the difficulties by employing polysacharides and biocompatible acrylate gels to encapsulate liposomes. Those methods have some shortcomings such as low liposome entrapment volume, the inability to immobilize pre-formed liposomes, and material instability at elevated temperatures. Recently, it is reported that liposomes can be immobilized in sol-gel glass by using sol-gel technology (U.S. Pat. No. 6,022,748 and PCT publication No. WO 97/26870). Liposome-containing sol-gel materials may offer the advantages of chemical and physical stabilization of the liposomes and allowing facile handling, and the opportunity of recovery and reuse. However, liposome-containing sol-gel materials may not be suitable for making medical devices such as ophthalmic lenses and implantable drug delivery device.
Thus, there is need for a material which comprise immobilized vesicles and is suitable for making a medical device (preferably an ophthalmic lens), an implantable device for localized drug delivery, or an in vivo biosensor. Such material can be easily tailored to entrap guest materials within a medical device or to delivery therapeutic agents at a localized site within a human body.
One object of the invention is to solve the above-mentioned difficulties in immobilizing liposomes and other vesicles to the surface of a solid-state material.
Another object of the invention is to provide a method for making a vesicle-containing material suitable for making a medical device.
A further object of the invention is to provide a vesicle-containing material that can carry a wide variety of guest materials having different functions and can find use in various biomedical applications, such as drug delivery, implantable sensors, and gene therapy.
A still further object of the invention is provide a medical device that contain vesicles carrying desired guest materials.